ENPP1 Research Articles

Role of ENPP1 in cancer pathogenesis: Mechanisms and clinical implications (Review).

Cancer is a significant societal, public health and economic challenge in the 21st century, and is the primary cause of death from disease globally. Ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) serves a crucial role in several biochemical processes, including adenosine triphosphate hydrolysis, purine metabolism and regulation of signaling pathways. Specifically, ENPP1, a type II transmembrane glycoprotein and key member of the ENPP family, may be upregulated in tumor cells and implicated in the pathogenesis of multiple human cancers. The present review provides an overview of the structural, pathological and physiological roles of ENPP1 and discusses the potential mechanisms of ENPP1 in the development of cancers such as breast, colon, gallbladder, liver and lung cancers, and also summarizes the four major signaling pathways in tumors. Furthermore, the present review demonstrates that ENPP1 serves a crucial role in cell migration, proliferation and invasion, and that corresponding inhibitors have been developed and associated with clinical characterization.

Prenatal Diagnosis and Management of Generalized Arterial Calcification of Infancy

BACKGROUND: Generalized arterial calcification of infancy is a rare genetic disorder that was first reported in 1899. Since then, slightly more than 200 cases have been documented. This rare autosomal recessive disorder occurs when the homozygous ENPP1 gene mutation is associated with abnormal calcification in the medium and large arteries in the fetus. Overall mortality in individuals with generalized arterial calcification of infancy is high (55%) before the age of 6 months, with 24.4% dying in utero. Due to the high mortality rate, there is a critical need for additional reports and research regarding generalized arterial calcification of infancy. CASE: We submit a case report of a child with generalized arterial calcification of infancy—a unique instance in which the diagnosis was established prenatally and treatment was initiated in utero. Patient care was continued through a multidisciplinary approach coordinated between specialists across India, Australia, and the United States. There was an almost complete resolution of the calcification, with near-normal development and intellectual capacity of the child for age. CONCLUSION: Clear guidelines are needed regarding prenatal use of bisphosphonate therapy, timing, dosage, and duration of treatment for fetuses with ENPP1 gene mutations to minimize disease progression and improve neonatal health at birth. This case further illustrates how involving well-informed parents in decision making can help tailor the appropriate treatment. Our report also describes the possibility of new, ongoing clinical trials that may pave the way for a cure for this child and others.

Homozygous splice-site variant in ENPP1 underlies generalized arterial calcification of infancy.

ENPP1 (ectonucleotide pyrophosphatase/phosphodiesterase 1) plays a critical role by converting extracellular ATP to AMP, generating extracellular PPi, a potential inhibitor of calcification. Pathogenic variants in the ENPP1 cause generalized arterial calcification of infancy (GACI [OMIM 208000]). GACI, is an ultra-rare disease characterized by early-onset calcification of large and medium-sized arteries, leading to severe cardiovascular complications such as heart failure, pulmonary stenosis (PS), hypertension, and more. In this study, we report a novel homozygous splice-site pathogenic variant in ENPP1 (NM_006208, c.2230 + 5G > A; p.Asp701Asnfs*2) residing in C-terminal nuclease-like domain (NLD) of ENPP1 protein in a Pakistani family diagnosed with severe valvular PS and mild right ventricular hypertrophy (RVH). cDNA assays confirmed the skipping of exon 21, and the splice product underwent nonsense-mediated decay. Functional studies on fibroblasts from the patient demonstrated increased calcification and decreased enzymatic activity of ENPP1, recapitulating the hallmarks of GACI. By combining genetic analysis with the in vitro study, we substantiate that ENPP1:c.2230 + 5G > A variant is pathogenic, underscoring its role in the development of GACI.

Identification of a pancreatic juice-specific fluorescent probe through 411 probes activated by aminopeptidases/proteases or phosphatases/phosphodiesterases

BackgroundThis study is a retrospective review aimed to identify pancreatic juice-specific fluorescent probes to visualize pancreatic juice using a library of 381 aminopeptidase/protease-activatable fluorescent probes and 30 phosphatase/phosphodiesterase probes. In 2013, we developed a fluorescence imaging technique using a chymotrypsin probe to visualize pancreatic juice, linked to postoperative pancreatic fistula (POPF). This probe required addition of trypsin to convert pancreatic chymotrypsinogen to chymotrypsin. Recently we accessed libraries of enzyme-activatable fluorescent probes to find specific probes that facilitated target-specific imaging. MethodsPancreatic juice and ascitic fluid samples were collected in eight patients undergoing pancreaticoduodenectomy. Reaction rates of pancreatic juice to background ascitic fluids were calculated for these 411 fluorescent probes. ResultsForty-four fluorescent probes were screened in terms of high reactivity with pancreatic juice. Only one candidate probe targeting ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) 1 was selected for a pancreatic juice-specific fluorescent probe. Inhibitor experiments and Western blotting supported the presence of ENPP1 in the pancreatic juice. ConclusionsENPP1-targeting fluorescent probe may have the potential to visualize pancreatic juice leakage during surgery. This finding may allow surgeons to suture close leaking sites and decide the necessity of prophylactic abdominal drains; however, the role of ENPP1 in pancreatic juice remains to be clarified.

7217 Impact of INZ-701 on Bone and Mineral Metabolism Biomarkers and Clinical Outcomes in Adults with ENPP1 Deficiency - Results from 48-week Phase 1/2 Open Label Study

Abstract Disclosure: K. Gunter: Employee; Self; Inozyme Pharma. Stock Owner; Self; Inozyme Pharma. R.A. Wermers: Research Investigator; Self; Inozyme Pharma. R. Fuhr: Employee; Self; Parexel GmbH. Research Investigator; Self; Inozyme Pharma. D. Schnabel: Research Investigator; Self; Inozyme Pharma. A. Besancon: Research Investigator; Self; Inozyme Pharma. M.A. Nour: Research Investigator; Self; Inozyme Pharma. D. Wenkert: Stock Owner; Self; Inozyme Pharma. Y. Sabbagh: Employee; Self; Inozyme Pharma. Stock Owner; Self; Inozyme Pharma. Background: ENPP1 Deficiency is a rare disorder due to inactivating mutations in the ENPP1 gene that result in low levels of inorganic pyrophosphate (PPi), a critical regulator of mineralization. Subsequent pathologic soft tissue calcification results in severe vascular calcification and ∼50% infant mortality. By early adolescence the majority of survivors develop FGF-23 mediated hypophosphatemic rickets, characterized by bone deformities, short stature, joint/ligament calcification and musculoskeletal pain. No targeted therapy exists for this disease. INZ-701 is a recombinant ENPP1-Fc investigational product. Purpose: To describe the safety, tolerability, immunogenicity, and exploratory efficacy (bone and mineral metabolism biomarkers and clinical outcomes) of INZ-701 in adults with ENPP1 Deficiency through the end of the phase 2 study period (week 48). Methods: Phase 1/2, multicenter, open-label, multiple ascending dose study including three adults in each of three dose cohorts (0.2, 0.6 and 1.8 mg/kg, total N=9) with genetic variants in ENPP1 and PPi <1300 nM (NCT04686175). Participants were dosed subcutaneously on Day 1, then twice weekly from Day 8 to end of study. Data through wk 48 as of July 6, 2023 are included; topline wk 48 data will be presented. Per protocol, participants may continue to receive INZ-701 beyond wk 48. Results: Rapid increase in mean PPi from baseline of 426±407 nM was noted in all patients, reaching the healthy volunteer range within 6 hrs of the first dose with sustained elevation through wk 48. Mean PPi across the 0.2, 0.6 and 1.8 mg/kg dose cohorts from day 32 to wk 48 was 1299±131 nM, 1356±136 nM, and 1282±81 nM, respectively. There were improvements from baseline to wk 48 in mean pooled FGF-23 (-22 pg/mL) and serum phosphate (+0.18 mg/dL), with dose-dependent changes in bone specific alkaline phosphatase consistent with bone healing. DEXA revealed improvements in spine BMD and BMC. There were trends towards improvement in mean % predicted change in 6MWT from baseline to wk 48: cohort 1, 76.7% (SE 10.5) to 85.0% (SE 3.0); cohort 2, 52.2% (SE 10.9 ) to 79.0% (SE 2.9); cohort 3, wk 48 data not available. Improvements were also observed in physician and patient global impression of change score (with no patients deteriorating) and PROMIS pain intensity score. INZ-701 was well tolerated with no drug-related serious or severe (> grade 2) adverse events. Low titers of non-neutralizing anti-drug antibodies (≤160) were observed in 7/9 patients. Long half-life of approximately 126 hours suggests the potential for once-weekly dosing. Conclusions: In adults with ENPP1 Deficiency, INZ-701 was well tolerated with no related serious or severe adverse events. INZ-701 demonstrated a rapid and sustained increase in PPi levels from baseline to week 48 with corresponding improvements in bone mineral biomarkers, functional performance, and patient and physician-reported outcomes. Presentation: 6/3/2024

12279 Molecular Strategy And Genetic Characterization Of A Large Cohort Of Pediatric Patients With Hereditary Hypophosphatemic Rickets: Advantages Of Next Generation Sequencing

Abstract Disclosure: N. Perez Garrido: None. P. Ramirez: None. G.L. Viterbo: None. M. del Pino: None. S. Abbate: None. N.I. Saraco: None. F. Tesan: None. M. Ciaccio: None. V. Fano: None. A. Belgorosky: None. R. Marino: None. Background: Hereditary hypophosphatemic rickets (HHR) is a group of rare disorders characterized by renal phosphate wasting and impairment of vitamin D metabolism. Different genetic defects can cause HHR, although they share similar clinical, radiological and biochemical features. Dominant X-linked HR (XLHR) is the most frequent form (1/ 20,000) caused by inactivating variants in PHEX gene. As affected individuals present with a broad phenotypic spectrum next generation sequencing (NGS) represent a useful tool for molecular diagnosis characterization. Aim: To report a molecular strategy and genetic characterization of a large cohort of pediatric patients with HHR followed in a single tertiary institution. Patients and Methods: We analyzed 77 affected patients from 60 non related families (and 58 parents) sent to our laboratory for molecular genetic testing under suspicion of HHR based on clinical, radiological and laboratory studies.In patients without hypercalciuria, Sanger sequencing of PHEX gene was initially performed. In female cases in which no alteration was detected, MLPA analysis was used to detect copy number variations. A group of patients with no proven variations in PHEX gene and those with hypercalciuria were analyzed using a NGS custom panel including 14 related genes. Results: Of the total 60 non related cases a pathogenic variant was found in 52 (87%). Regarding PHEX gene analysis, a pathogenic variant was found in 48/60 (80%), 27 were sporadic and 21 familial cases. Forty-one different pathogenic variants were found (5 gross deletions, 13 nonsense, 9 frameshift, 5 splice-site and 9 missense) distributed throughout the gene with higher prevalence from exon 15 to 22. 18/41 (44%) of variants were novel. RNA analysis was performed in 2 novel splice variants (c.849G>A-p.Glu283Glu and c.1586+6T>A) in which an abnormal splicing was confirmed.We found a pathogenic variant in 5/9 cases analyzed by NGS. Three of them in SLC34A3 gene (2 homozygous, 1 compound heterozygous), 1 in ENPP1 gene (compound heterozygous) and 1 in PHEX gene non-detected by Sanger sequencing. Discussion: This molecular strategy, along with a careful clinical and biochemical selection of patients, allowed us to perform genetic diagnosis in 87 % of non-related families. This study reports 21 novel pathogenic variants and it shows the greatest genetic characterization in pediatric HHR patients in Argentine population. The results obtained confirmed that PHEX is the most responsible gene for HHR phenotype, as previously described. By NGS, less common forms of rickets could be detected. Among them, the most frequent was HHR with hypercalciuria due to recessive mutations in SLC34A3 gene. NGS studies represent a useful tool, especially in those complex cases, to reach an accurate diagnosis, and they contribute to improve long term follow up of patients and genetic counseling. Presentation: 6/2/2024

Discovery of orally bioavailable phosphonate prodrugs of potent ENPP1 inhibitors for cancer treatment

Ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) is the dominant hydrolase of 2′,3′-cyclic GMP-AMP (cGAMP). Inhibition of ENPP1 contributes to increased cGAMP concentration and stimulator of interferon gene (STING) activation, with the potential to boost immune response against cancer. ENPP1 is a promising therapeutic target in tumor immunotherapy. To date, orally bioavailable ENPP1 inhibitors with highly potent activity under physiological conditions have been rarely reported. Herein, we report our effort in the design and synthesis of two different series of ENPP1 inhibitors, and in the identification of a highly potent ENPP1 inhibitor 27 (IC50 = 1.2 nM at pH 7.5), which significantly enhanced the cGAMP-mediated STING activity in THP-1 cells. Phosphonate compound 27 has good preclinical pharmacokinetic profiles with low plasma clearance rate in mouse, rat, and dog. It has been developed as bis-POM prodrug 36 which successfully improves the oral bioavailability of 27. In the Pan02 syngeneic mouse model of pancreatic cancer, orally administered 36 showed synergistic effect in combination with radiotherapy.

Regulation of TGF-β1-induced fibroblast differentiation of human periodontal ligament stem cells through the mutually antagonistic action of ectonucleotide pyrophosphatase/phosphodiesterase 1 and 2.

Human periodontal ligament stem cells (hPDLSCs) differentiate into periodontal ligament (PDL) fibroblasts, osteoblasts, and cementoblasts. To identify inducers of PDL fibroblastic differentiation, monoclonal antibody series were developed a series of against membrane/extracellular matrix (ECM) molecules through decoy immunization. The anti-PDL13 antibody targets ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), renowned for regulating skeletal and soft tissue mineralization. ENPP1 accumulates in the periodontal ligament region of tooth roots, and specifically localizes to the cell boundaries and elongated processes of the fibroblastic cells. As ENPP1 expression increases during fibroblastic differentiation, mineralization induced by tissue-nonspecific alkaline phosphatase (TNAP), a pyrophosphate-degrading enzyme, is completely inhibited. This is consistent with ENPP1 and TNAP acting in opposition, and TGF-β1-induced ENPP1 expression creates an essential environment for PDL fibroblast differentiation. Representative fibroblastic differentiation markers decrease with endogenous ENPP1 inhibition by siRNA and antibody blocking. ENPP2 generates lipid signaling molecules. In contrast to ENPP1, ENPP2 disappears in TGF-β1-induced PDL fibroblasts. Ectopic expression of ENPP2 hinders TGF-β1-induced PDL fibroblastic differentiation. Suppression of ENPP1 and ENPP2 leads to severe defects in undifferentiated and differentiated cells, demonstrating that these two factors play opposing roles in soft and hard tissue differentiation but can complement each other for cell survival. In conclusion, increased ENPP1 is crucial for TGF-β1-induced PDL differentiation, while ENPP2 and TNAP can inhibit ENPP1. ENPP1 and ENPP2 exhibit complementary functions in the cell survival.

Autosomal recessive hypophosphatemic rickets type 2 due to ENPP1 deficiency (ARHR2)

Autosomal recessive hypophosphatemic rickets type 2 (ARHR2; MIM #613312) is a very rare disorder caused by biallelic loss-of-function mutations in the ENPP1 (ectonucleotide pyrophosphatase/phosphodiesterase 1) gene. ENPP1 deficiency encompasses a spectrum of phenotypes that includes, in addition to ARHR2, generalized arterial calcification of infancy (GACI), ossification of the posterior longitudinal ligament (OPLL), and pseudoxanthoma elasticum. ARHR2 can be found in GACI survivors, but it may also be the first manifestation of ENPP1 deficiency. Although the precise mechanisms are not fully elucidated, patients with GACI and ARHR2 have elevated serum FGF23 levels, leading to renal phosphate wasting and hypophosphatemia. As a result, the clinical and radiological phenotype of ARHR2 patients is very similar to that of patients affected with other forms of hypophosphatemic rickets, such as X-linked hypophosphatemia. Patients show signs of rickets (abnormal mineralization of growth plates in children) and osteomalacia (abnormal bone mineralization in children and adults) of varying severity. Clinical manifestations specific to ENPP1 loss-of-function mutations and common to GACI, such as ectopic calcifications (valvular, arterial, or periarticular), deafness, OPLL, and PXE, may also be found. Genetic confirmation of the disease is important so as to ensure that patients receive the appropriate treatment or have the opportunity to participate in clinical trials to evaluate the safety and efficacy of novel and promising recombinant enzyme therapies.

Clinical presentation and burden of ENPP1 deficiency in adults

While the clinical consequences of severe ENPP1 deficiency leading to the rare disorders generalized arterial calcification of infancy (GACI) and autosomal recessive hypophosphatemic rickets type 2 (ARHR2) are well defined and understood, much less is known about how this evolves into adulthood and how moderate ENPP1 deficiency can first manifest in adulthood. Moreover, growing evidence substantiates an association of genetic variants in the ENPP1 gene with a wide range of further clinical manifestations including early-onset osteoporosis, osteoarthritis, and different forms of spinal ligament calcifications, i.e., diffuse idiopathic skeletal hyperostosis (DISH) and ossification of the posterior/anterior longitudinal ligament (OPLL/OALL). Furthermore, conditions with primarily extraskeletal signs and symptoms such as Cole disease, coagulopathies, and metabolic syndrome can seemingly result from ENPP1 variants. The causality and the pathophysiology behind these different clinical presentations appear complex and require further research, especially since the coincidence of these different phenotypes is rarely described and available evidence suggests that part of the aforementioned manifestations may result from ENPP1 effects beyond the catalytic activity of processing ATP to AMP and inorganic pyrophosphate (PPi). Growing awareness of the additional ENPP1-related manifestations across the lifespan will advance our understanding of this complex condition and help to standardize diagnostic approaches and develop individually tailored treatment concepts.

Activation of Nuclear Factor Erythroid 2-Related Factor 2 Transcriptionally Upregulates Ectonucleotide Pyrophosphatase/Phosphodiesterase 1 Expression and Inhibits Ectopic Calcification in Mice.

Calcification plays a key role in biological processes, and breakdown of the regulatory mechanism results in a pathological state such as ectopic calcification. We hypothesized that ENPP1, the enzyme that produces the calcification inhibitor pyrophosphate, is transcriptionally regulated by Nrf2, and that Nrf2 activation augments ENPP1 expression to inhibit ectopic calcification. Cell culture experiments were performed using mouse osteoblastic cell line MC3T3-E1. Nrf2 was activated by 5-aminolevulinic acid and sodium ferrous citrate. Nrf2 overexpression was induced by the transient transfection of an Nrf2 expression plasmid. ENPP1 expression was monitored by real-time RT-PCR. Because the promoter region of ENPP1 contains several Nrf2-binding sites, chromatin immunoprecipitation using an anti-Nrf2 antibody followed by real-time PCR (ChIP-qPCR) was performed. The relationship between Nrf2 activation and osteoblastic differentiation was examined by alkaline phosphatase (ALP) and Alizarin red staining. We used mice with a hypomorphic mutation in ENPP1 (ttw mice) to analyze whether Nrf2 activation inhibits ectopic calcification. Nrf2 and Nrf2 overexpression augmented ENPP1 expression and inhibited osteoblastic differentiation, as indicated by ALP expression and calcium deposits. ChIP-qPCR showed that some putative Nrf2-binding sites in the ENPP1 promoter region were bound by Nrf2. Nrf2 activation inhibited ectopic calcification in mice. ENPP1 gene expression was transcriptionally regulated by Nrf2, and Nrf2 activation augmented ENPP1 expression, leading to the attenuation of osteoblastic differentiation and ectopic calcification in vitro and in vivo. Nrf2 activation has a therapeutic potential for preventing ectopic calcification.

Generalized arterial calcification of infancy due to mutations of the ENPP1 and ABCC6 genes: phenotype features, bisphosphonate therapy

Generalized arterial calcification of infancy due to mutations of the ENPP1 and ABCC6 genes: phenotype features, bisphosphonate therapy

Ectonucleotidase inhibitors: targeting signaling pathways for therapeutic advancement-an in-depth review.

Ectonucleotidase inhibitors are a family of pharmacological drugs that, by selectively targeting ectonucleotidases, are essential in altering purinergic signaling pathways. The hydrolysis of extracellular nucleotides and nucleosides is carried out by these enzymes, which include ectonucleoside triphosphate diphosphohydrolases (NTPDases) and ecto-5'-nucleotidase (CD73). Ectonucleotidase inhibitors can prevent the conversion of ATP and ADP into adenosine by blocking these enzymes and reduce extracellular adenosine. These molecules are essential for purinergic signaling, which is associated with a variability of physiological and pathological processes. By modifying extracellular nucleotide metabolism and improving purinergic signaling regulation, ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) inhibitors have the potential to improve cancer treatment, inflammatory management, and immune response modulation. Purinergic signaling is affected by CD73 inhibitors because they prevent AMP from being converted to adenosine. These inhibitors are useful in cancer therapy and immunotherapy because they may improve chemotherapy effectiveness and alter immune responses. Purinergic signaling is controlled by NTPDase inhibitors, which specifically target enzymes involved in extracellular nucleotide breakdown. These inhibitors show promise in reducing immunological responses, thrombosis, and inflammation, perhaps assisting in the treatment of cardiovascular and autoimmune illnesses. Alkaline phosphatase (ALP) inhibitors alter the function of enzymes involved in dephosphorylation reactions, which has an impact on a variety of biological processes. By altering the body's phosphate levels, these inhibitors may be used to treat diseases including hyperphosphatemia and certain bone problems. This article provides a guide for researchers and clinicians looking to leverage the remedial capability of ectonucleotidase inhibitors in a variety of illness scenarios by illuminating their processes, advantages, and difficulties.

Inhibition of Vascular Smooth Muscle Cell Proliferation by ENPP1: The Role of CD73 and the Adenosine Signaling Axis.

The Ectonucleotide Pyrophosphatase/Phosphodiesterase 1 (ENPP1) ectoenzyme regulates vascular intimal proliferation and mineralization of bone and soft tissues. ENPP1 variants cause Generalized Arterial Calcification of Infancy (GACI), a rare genetic disorder characterized by ectopic calcification, intimal proliferation, and stenosis of large- and medium-sized arteries. ENPP1 hydrolyzes extracellular ATP to pyrophosphate (PPi) and AMP. AMP is the precursor of adenosine, which has been implicated in the control of neointimal formation. Herein, we demonstrate that an ENPP1-Fc recombinant therapeutic inhibits proliferation of vascular smooth muscle cells (VSMCs) in vitro and in vivo. Addition of ENPP1 and ATP to cultured VSMCs generated AMP, which was metabolized to adenosine. It also significantly decreased cell proliferation. AMP or adenosine alone inhibited VSMC growth. Inhibition of ecto-5'-nucleotidase CD73 decreased adenosine accumulation and suppressed the anti-proliferative effects of ENPP1/ATP. Addition of AMP increased cAMP synthesis and phosphorylation of VASP at Ser157. This AMP-mediated cAMP increase was abrogated by CD73 inhibitors or by A2aR and A2bR antagonists. Ligation of the carotid artery promoted neointimal hyperplasia in wild-type mice, which was exacerbated in ENPP1-deficient ttw/ttw mice. Prophylactic or therapeutic treatments with ENPP1 significantly reduced intimal hyperplasia not only in ttw/ttw but also in wild-type mice. These findings provide the first insight into the mechanism of the anti-proliferative effect of ENPP1 and broaden its potential therapeutic applications beyond enzyme replacement therapy.

T Cell-Derived Apoptotic Extracellular Vesicles Hydrolyze cGAMP to Alleviate Radiation Enteritis via Surface Enzyme ENPP1.

Radiation enteritis is the most common complication of pelvic radiotherapy, but there is no effective prevention or treatment drug. Apoptotic T cells and their products play an important role in regulating inflammation and maintaining physiological immune homeostasis. Here it is shown that systemically infused T cell-derived apoptotic extracellular vesicles (ApoEVs) can target mice irradiated intestines and alleviate radiation enteritis. Mechanistically, radiation elevates the synthesis of intestinal 2'3' cyclic GMP-AMP (cGAMP) and activates cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) proinflammatory pathway. After systemic infusion of ApoEVs, the ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) enriches on the surface of ApoEVs hydrolyze extracellular cGAMP, resulting in inhibition of the cGAS-STING pathway activated by irradiation. Furthermore, after ApoEVs are phagocytosed by phagocytes, ENPP1 on ApoEVs hydrolyzed intracellular cGAMP, which serves as an intracellular cGAMP hydrolyzation mode, thereby alleviating radiation enteritis. The findings shed light on the intracellular and extracellular hydrolysis capacity of ApoEVs and their role in inflammation regulation.

Synovial Membrane Is a Major Producer of Extracellular Inorganic Pyrophosphate in Response to Hypoxia.

Calcium pyrophosphate dehydrate (CPPD) crystals are found in the synovial fluid of patients with articular chondrocalcinosis or sometimes with osteoarthritis. In inflammatory conditions, the synovial membrane (SM) is subjected to transient hypoxia, especially during movement. CPPD formation is supported by an increase in extracellular inorganic pyrophosphate (ePPi) levels, which are mainly controlled by the transporter Ank and ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1). We demonstrated previously that transforming growth factor (TGF)-β1 increased ePPi production by inducing Ank and Enpp1 expression in chondrocytes. As the TGF-β1 level raises in synovial fluid under hypoxic conditions, we investigated whether hypoxia may transform SM as a major source of ePPi production. Synovial fibroblasts and SM explants were exposed to 10 ng/mL of TGF-β1 in normoxic or hypoxic (5% O2) culture conditions. Ank and Enpp1 expression were assessed by quantitative PCR, Western blot and immunohistochemistry. ePPi was quantified in culture supernatants. RNA silencing was used to define the respective roles of Ank and Enpp1 in TGF-β1-induced ePPi generation. The molecular mechanisms involved in hypoxia were investigated using an Ank promoter reporter plasmid for transactivation studies, as well as gene overexpression and RNA silencing, the respective role of hypoxia-induced factor (HIF)-1 and HIF-2. Our results showed that TGF-β1 increased Ank, Enpp1, and therefore ePPi production in synovial fibroblasts and SM explants. Ank was the major contributor in ePPi production compared to ENPP1. Hypoxia increased ePPi levels on its own and enhanced the stimulating effect of TGF-β1. Hypoxic conditions enhanced Ank promoter transactivation in an HIF-1-dependent/HIF-2-independent fashion. We demonstrated that under hypoxia, SM is an important contributor to ePPi production in the joint through the induction of Enpp1 and Ank. These findings are of interest as a rationale for the beneficial effect of anti-inflammatory drugs on SM in crystal depositions.

Quantitative correlation of ENPP1 pathogenic variants with disease phenotype

Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) codes for a type 2 transmembrane glycoprotein which hydrolyzes extracellular phosphoanhydrides into bio-active molecules that regulate, inter alia, ectopic mineralization, bone formation, vascular endothelial proliferation, and the innate immune response. The clinical phenotypes produced by ENPP1 deficiency are disparate, ranging from life-threatening arterial calcifications to cutaneous hypopigmentation. To investigate associations between disease phenotype and enzyme activity we quantified the enzyme velocities of 29 unique ENPP1 pathogenic variants in 41 patients enrolled in an NIH study along with 33 other variants reported in literature. We correlated the relative enzyme velocities with the presenting clinical diagnoses, performing the catalytic velocity measurements simultaneously in triplicate using a high-throughput assay to reduce experimental variation. We found that ENPP1 variants associated with autosomal dominant phenotypes reduced enzyme velocities by 50 % or more, whereas variants associated with insulin resistance had non-significant effects on enzyme velocity. In Cole disease the catalytic velocities of ENPP1 variants associated with AD forms trended to lower values than those associated with autosomal recessive forms – 8-32 % vs. 33 % of WT, respectively. Additionally, ENPP1 variants leading to life-threatening vascular calcifications in GACI patients had widely variable enzyme activities, ranging from no significant differences compared to WT to the complete abolishment of enzyme velocity. Finally, disease severity in GACI did not correlate with the mean enzyme velocity of the variants present in affected compound heterozygotes but did correlate with the more severely damaging variant. In summary, correlation of ENPP1 enzyme velocity with disease phenotypes demonstrate that enzyme velocities below 50 % of WT levels are likely to occur in the context of autosomal dominant disease (due to a monoallelic variant), and that disease severity in GACI infants correlates with the more severely damaging ENPP1 variant in compound heterozygotes, not the mean velocity of the pathogenic variants present.

Identification of the extracellular membrane protein ENPP3 as a major cGAMP hydrolase and innate immune checkpoint

2'3'-Cyclic guanosine monophosphate (GMP)-AMP (cGAMP) is a second messenger synthesized upon detection of cytosolic double-stranded DNA (dsDNA) and passed between cells to facilitate downstream immune signaling. Ectonucleotide pyrophosphatase phosphodiesterase I (ENPP1), an extracellular enzyme, was the only metazoan hydrolase known to regulate cGAMP levels to dampen anti-cancer immunity. Here, we uncover ENPP3 as the second and likely the only other metazoan cGAMP hydrolase under homeostatic conditions. ENPP3 has a tissue expression pattern distinct from ENPP1's and accounts for all cGAMP hydrolysis activity in ENPP1-deficient mice. Importantly, we also show that, as with ENPP1, selectively abolishing ENPP3's cGAMP hydrolysis activity results in diminished cancer growth and metastasis of certain tumor types in a stimulator of interferon genes (STING)-dependent manner. Both ENPP1 and ENPP3 are extracellular enzymes, suggesting the dominant role that extracellular cGAMP must play as a mediator of cell-cell innate immune communication. Our work demonstrates that ENPP1 and ENPP3 non-redundantly dampen extracellular cGAMP-STING signaling, pointing to ENPP3 as a target for cancer immunotherapy.

Bioactivity of 2-(3,4-Dihydroxyphenyl)-5,7-dihydroxy-2,3-dihydrochromen-4-one from pistacia chinensis on ENPP1 and aldose reductase

Pistacia chinensis is used as a decorative tree and currently studied as a source of biofuels. Besides, its parts and extracts are endowed with several therapeutic uses which have been widely explored in traditional medicine and that are related to its rich composition in phytochemicals. Molecular docking and enzymatic inhibition tests were used to study the activity of eriodictyol, a flavonoid extracted from the barks of P. chinensis, against ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) and aldose reductase (ALR2). The compound was highlighted as a micromolar inhibitor in vitro (IC50 = 263.76 ± 1.32 µM and 4.21 ± 0.94 µM, respectively) and docking showed that eriodictyol efficiently targets the binding sites of the enzymes. In conclusion, this study unveils the potential of eriodictyol on enzymes that are involved in immunostimulation and in complications of diabetes mellitus.

Abstract CT161: First-in-human study of ENPP1 inhibitor, SR-8541A, for the treatment of solid tumors

Abstract Purpose: Compelling evidence suggests that careful and therapeutically relevant activation of the STING (STimulator of INterferon Genes) pathway is vital to elicit potent anti-cancer innate immune responses. STING is widely expressed and targeting it directly poses many challenges, including systemic activation of interferon. Therefore, alternative approaches to activate STING in a controlled manner may generate a better therapeutic response in cancer patients. Ectonucleotide Pyrophosphatase/Phosphodiesterase-1 (ENPP1) is the direct negative regulator of the STING pathway that hydrolyzes 2’3’ cGAMP, the direct activator of STING. Highest levels of 2′3′ cGAMP can be found in tumors and recent evidence suggests that 2′3′ cGAMP acts locally, as a paracrine immune transmitter. Recent studies have also reported elevated ENPP1 expression in metastatic tumors. We hypothesize that inhibiting ENPP1 with a small molecule inhibitor may produce superior outcomes by activating STING in the tumor microenvironment. We have developed SR-8541A, a highly selective and potent inhibitor of ENPP1. Our initial work to support the development of SR-8541A consisted of pharmacodynamics studies, bioanalytical development, pharmacokinetics (PK) and non-GLP toxicology studies in three species, a GLP repeat dose dog telemetry study, and 28-day GLP toxicology studies in rats and dogs including toxicokinetic (TK) analyses. Here we report initial findings from our ongoing first in human, phase I trial of SR-8541A in advanced metastatic solid tumors. Methods: This study is evaluating the safety, tolerability, and pharmacokinetics (PK) of SR-8541A administered orally as a monotherapy in subjects with solid tumors which are refractory to standard therapeutic options, or for which there are no standard therapeutic options (NCT06063681). The primary objective of the study is to characterize the safety, tolerability, DLTs, maximum tolerated dose and RP2D and schedule for future studies of SR-8541A. Secondarily, the study aims to evaluate the PK and efficacy per RECIST of SR-8541A. SR-8541A is administered orally in 28-day cycles and is following an accelerated titration dose (ATD) escalation. Blood samples are being collected for PK assessment, target engagement, and biomarker assessment. Results: Sample analysis from a subject treated with SR-8541A (5 mg) in the ATD portion of the study is ongoing. No treatment-related adverse events have been reported. No dose-limiting toxicities occurred during the 28-day DLT period. Plasma drug levels collected for the PK show cMAX concentrations in the projected therapeutic dose range. Biomarker assessment is ongoing and will be included in the presentation. The SR-8541A dose has escalated and the study is currently enrolling at the 10 mg dose. Conclusions: The first evaluated dose of SR-8541A has shown to be safe and well tolerated. Pharmacokinetic data shows strong oral bioavailability and supports escalation in the phase I trial and continued assessment of SR-8541A in the clinic. Citation Format: Alexis S. Weston, Trason Thode, Monil Shah, Amanda Seiz, Jonathan Northrup, Srinivas Kasibhatla, Mohan Kaadige, Sunil Sharma. First-in-human study of ENPP1 inhibitor, SR-8541A, for the treatment of solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT161.